Nori is a red seaweed from the genus Porphyra that is commonly used in the making of sushi. This seaweed grows throughout the temperate regions of the world and has long been eaten by people in Japan, China and Korea, where it is grown commercially. This alga has also been eaten by the indigenous peoples of the American Northwest and parts of the British Isles.Nutritional ContentNori contains between 30 and 50 percent protein and is fairly low in sodium because most of the salt is washed away during processing. It is a good source of vitamin A, folate and niacin. Fresh nori is a good source of vitamin C, but the shelf life for this nutrient after processing is fairly short. A 2007 Venezuelan study published in the "Journal of Nutrition" stated that nori is a valuable source of iron for people eating rice-based meals and that, unlike many grains and beans, it does not contain phytates, which can bind with other nutrients and slow down their absorption.NORI AND BREAST CANCERA Korean study published in the May 2010 issue of the "British Journal of Nutrition" examined the effects of seaweed consumption on breast cancer rates. In this study, women with breast cancer were matched to healthy controls according to age and menopausal status. Both groups of women were asked to complete food frequency questionnaires, which were then subjected to statistical analysis. The data showed that frequent consumption of nori seaweed was associated with lower rates of breast cancer for both pre-menopausal and menopausal women.NORI AND CHOLESTEROLA Japanese study published in the June 2001 issue of the "British Journal of Nutrition" reported on the effects of either nori or kombu seaweed on cholesterol levels in male rats. Rats fed the non-cholesterol containing diets and kombu showed higher levels of cholesterol than their counterparts not receiving seaweed. The nori-fed rats showed no change. However, when rats fed the cholesterol-rich diet were examined, those fed nori showed lower cholesterol levels than those fed kombu. The results suggest that nori consumption could have a beneficial effect on cholesterol levels.VITAMIN B12Nori is reputed to contain vitamin B12 as one of its nutrients, but this claim is highly controversial because some substances that look like vitamin B12 in laboratory tests don't work like B12 in the body. True vitamin B12 reduces the levels of a substance called methylmalonic acid, which is a waste product excreted in the urine when B12 is not available. A 2001 study published in the "British Journal of Nutrition" reported that vitamin B12-deficient rats fed nori seaweed showed reduced methylmalonic acid excretion. However, studies have not, as of 2011, demonstrated the same effect in humans.